Erixon K, Renger G
Max Volmer Institut für Physikalische Chemie und Molekularbiologie der Technischen Universität, Berlin, Germany.
Biochim Biophys Acta. 1974 Jan 18;333(1):95-106. doi: 10.1016/0005-2728(74)90166-2.
The effect of tetraphenylboron on the O2 evolution, the electron transport in normal and in Tris-washed chloroplasts, and on the decay of the electrical field across the thylakoid membrane has been investigated in spinach chloroplasts. It was found that: (1) The average O2 yield per flash as a function of the tetraphenylboron concentration is dependent on the number of excitation flashes. With increasing flash number, the tetraphenylboron concentration which is required for 50% suppression of the average O2 yield per flash shifts toward higher values. (2) After the irreversible consumption of tetraphenylboron by System II oxidizing equivalents, the O2 evolution reappears. (3) The electron flow from System II to System I, as indicated by the amplitude of the reduction kinetics of the 703 nm absorption change, remains unaffected in the tetraphenylboron concentration range and at flash numbers where the O2 evolution is totally suppressed. (4) Tetraphenylboron restores electron transport in Tris-washed chloroplasts. This tetraphenylboron-mediated electron transport is completely blocked by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). (5) Preliminary titration experiments favor the assumption that tetraphenylboron acts in chloroplasts rather as a 1-electron donor than as a 2-electron donor. (6) Tetraphenylboron accelerates the decay of the electrical field across the thylakoid membrane. Because of its ability to act as a System II electron donor, the accelerating effect on the electrical field is transitory if System II is active. By contrast, in DCMU-blocked chloroplasts with active System I electron transport [mediated by the 2,6-dichlorophenolindophenol (DCIP) cycle], a permanent accelerating effect on the electrical field is observed. From these results it has been concluded, that tetraphenylboron acts as an efficient 1-electron donor for System II. The functional integrity of the water-splitting enzyme system Y is not required for this donation. Tetraphenylboron itself does not destroy the O2 evolution capability of chloroplasts, it rather acts as a competitive electron donor. However, an inhibitory effect arises probably from the oxidation products of tetraphenylboron. The possible modes of action of tetraphenylboron are discussed.
研究了四苯基硼对菠菜叶绿体中氧气释放、正常及经Tris洗涤的叶绿体中的电子传递以及类囊体膜上电场衰减的影响。结果发现：（1）每次闪光的平均氧气产量作为四苯基硼浓度的函数取决于激发闪光的次数。随着闪光次数增加，使每次闪光的平均氧气产量抑制50%所需的四苯基硼浓度向更高值移动。（2）在系统II氧化当量不可逆地消耗四苯基硼后，氧气释放重新出现。（3）如703nm吸收变化的还原动力学幅度所示，从系统II到系统I的电子流在四苯基硼浓度范围内以及在氧气释放被完全抑制的闪光次数下不受影响。（4）四苯基硼可恢复经Tris洗涤的叶绿体中的电子传递。这种由四苯基硼介导的电子传递被3-(3,4-二氯苯基)-1,1-二甲基脲（DCMU）完全阻断。（5）初步滴定实验支持这样的假设，即四苯基硼在叶绿体中作为单电子供体而非双电子供体起作用。（6）四苯基硼加速类囊体膜上电场的衰减。由于其作为系统II电子供体的能力，如果系统II活跃，对电场的加速作用是短暂的。相比之下，在具有活跃的系统I电子传递[由2,6-二氯酚靛酚（DCIP）循环介导]的DCMU阻断的叶绿体中，观察到对电场的永久加速作用。从这些结果得出结论，四苯基硼作为系统II的有效单电子供体起作用。这种供体作用不需要水裂解酶系统Y的功能完整性。四苯基硼本身不会破坏叶绿体的氧气释放能力，它更像是竞争性电子供体。然而，抑制作用可能源于四苯基硼的氧化产物。讨论了四苯基硼可能的作用方式。
